Electron discharge tube



Aug. 3, 1937. A. A. THOMAS ELECTRON DISCHARGE TUBE Filed May 16, 1936 /Uy f Patented Aug. 3, 1937 `\PATENT OFFICE v ELECTRON DISCHARGE TUBE Adolph A. Thomas, New York, N. Y., assigner to Radio Corporation of America, New York, N. Y.,

a corporation of Delaware Application May 16,

- 14 Claims. My invention. is for an electron discharge tube of novel construction and. 'possessingcertain .Y practical advantages over 'priorf'devices of this type. One object of. this invention isV to improve the manufacture of electronrtubes having a metal envelope'by reducing thenuinberoi' parts and l facilitating .the mounting-and', assembly of the variouselements,.l particularly as regards the i'n` I y lil Sulation'of t'heelectrode-supporting `rods or lead` 'in 'wir-es.` `Another object of myinvention isrto improvethe operation of "metal electron tubes, especially those used in radio `apparatus,' by

-1eliminatingor greatly lessening -the .tendency of fthe metal envelope to give off gas-'from its inner surface.

f The-all-metal radio tubes which have recently come. into use comprise an vo uter metal shell and a metal base disk sealed together. This metal 'disk carries the conducting rods or lead-in wires connected to the: electrode assembly, and each wire must be carefully insulated from'themetal o f the disk. According to. present practice,v this.

insulatlonvrequires janlalloy eyelet'A `vwelded .around a hole inthe metal` disk, `therebeing. a hole'for keach wire," and the wire passing through the, eye'- let is sealed thereto .byl'afsmall'thin sleeve ofk glass which constitutes the,.only insulation between the lead-in` V.wire and the `metal disk. Aside from the cost of thus` insulating each wire separately from the-metal walls of thev tube, there is the danger that any oneof these thinvglass sleeves might crack or a current of high voltage might leap across a glass sleeve to the grounded metal of the base disk and put the tube out of 0 commission.-

Further, in testing the behavior of all-metal radio tubes during operation, it has been found that the inner-metalsurface of the envelope or shell has a tendency to give. off gases-which re- 40 duce the efficiency of the tube or otherwise interfere with its proper functioning. Thus, although metal-radio tubes as heretofore'made have the adj vantage of ,mechanical strength and electrical self-shielding as compared with thev old glass tubes. the use of a metalenvelope and base has the double disadvantage `of-increasing the manufacturing cost` of the tube and'of gradually de-` teriorating the vacuum] in the metal-walled 50 chamber.

To overcome the afore-xnentioned and other disadvantages inherent inl prior all-metal radio tubes, I have devised a new electronv tube consisting of a metal shell and an insulating base v 193s, kserial No. soms (ci. l25o-27.5)

. metallic shell or envelope and the insulating base disk are sealed together. by an interposed ring of glass which is fused into place to vform a permanent. vacuum-tight weld of ample mechanical strength.. The lead-in wires or .rods .connected tothe electrode assembly pass through holes-in the insulating `disk to` which they are sealed by small. cylinders of fusedglasa and no separate insulation-ofvthese wires is necessary. l The in-1 sulating disk,' being sufliciently thick and strong, may al-so support the outer contact-pins of the .'tube;A sov that no separate base member for the pins is needed, as' in prior tubes. This base disk may be'molded or pressed of glass having a low expansion coefficient, or of vitreous ceramic material like porcelain, which is amply'strong when thickand is practically unaffected bygheat.' The innery surface of themetal shell is preferably A electroplated to provide a` `smooth dense wall ,adapted to prevent (or at least minimize)4 theocclusion andjcs'ubsequent liberation of gases. The l, metal shell'at its base encloses the insulating -l disk` andr fully protects it, so that the tube is` practically as strong as if made wholly ofmetal, yet is `cheaper t o make .and more satisfactory in its operation.4 i', i y The variousnovel features andadvantages of "my inventiongwillbe understood from/a descrip-v tionjof'the'accompanying'drawing.' in-which .Flrggl' Vrepre'sei'its a vertical section' of `an electroni discharge tube made according to" my in vention; "-.W' Fig. 2 shows how the metal shell 'and`1 theinvs'ulating'diskare sealed together;

Fig. 6 isqan enlarged fragmentary view showy ving how the lead-in wiresv and contact pins' are Asealed tothe insulating'disk; and

' Figs. 7-8 show different ways of mounting the .contact .pins in the insulating disk. f

Referring to-Fig. l, the outer structure of the electron tube consists of two main parts, a cylindrical shell or envelope I0 of sheet metal and a base disk I2 of insulating material of the `'vitreous type, such as glass or porcelain. The metal shell i0 may be of steel, nickel, duralumin, or an iron-nickel alloy with a low expansion co- ,eilicient--tov mentiononly a few of the commercially available metals. Personally I regard steel as the best metal to use on account of its strength and cheapness, but an iron-nickel alloy of approximately 63%. iron and 37% nickel has certain. advantages. as I shall point out later.

The base end of metal shell I0 is formed with an outer lateral shoulder I3 and a cylindrical flange Il, which preferably has an outwardly flaring edge il and terminates in an inwardly turned rim I6. The parts I3-I6 form an annular recess I1 which is completely filled by a seal Il of glass or similar material fused in position and uniting the vitreous disk I2 to the metal shell I0 by a strong vacuum-tight joint. Ihe disk I2 is preferably formed with a peripheral recess I8 to provide a circular shoulder 2li which locks the disk in the fused mass of the sealing ring I8. The inturned rim I6 on the lower end of metal shell III locks the seal I8 permanently in place.

It should be noted that the fused sealing ring Il contacts the adjacent walls of parts I8 and I2 along wide areas, thereby producing a weld of ample strength to unite the metal shell Iii and the insulating disk I2 into a substantially integral vacuum-tight enclosure. The rim I6 of metal shell I0 encloses the edge of seal I8 for protection, this rim being preferably embedded in the fused seal to make it flush with the underside of the seal and disk I2. In other words, the underside of the tube may be a perfectly fiat surface which permits the tube to be firmly mounted on a fiat support.

Fig. 2 illustrates a simple method of fusing the glass ring I8 in position. The metal shell I0 is held upside down in a cylindrical support 2l suitably mounted for slow rotation, the shoulder I3 of the shell resting on the top rim 22 of the support. The vitreous disk I2 (carrying the electrode assembly) is placed centrally over the inverted shell I0. the edge of the disk resting on shoulder I3 of the shell. The glass sealing ring I8 (cut to the right width from a glass cylinder) is placed in the annular recess I1 formed between the flange I4 of shell I0 and the periphery of disk I2. As the support 2| is rotated, gas jets 23 heat the metal ange I4 and the glass ring I8, which melts in the final heating stage and flows into the recess I1, completely filling it. The hardened mass of seal I8 remains in strong vacuum-tght adhesion to the adjacent walls of metal shell I0 and vitreous disk I2.

When the sealing operation is finished, an ejector 24 lifts up the tube for easy removal from support 2l. The ejector 2|, which may be a vertically movable rod or piston, engages the tubulation 25 formed integral with the domeshaped top of metal shell III. The tubulation 25 connects the interior of the tube with a suitable source of exhaust, and after the desired vacuum has been attained the tubulation is sealed off in any practical way, as will be understood without further explanation. The sealed tubulation or tip is shown at 25' in Fig. l. If it is desired to conceal the tip 28 in the commercial embodiment of the tube, the top of shell I0 is formed with a depression 28 around the tip and this depression may be filled with suitable plastic material 21, which rounds off the dome of the shell and hides the exhaust tip. The filler 21 may be glass, an aldehyde condensation product, ceramic material, or the like. If this dome-shaped filler is colored, it may also serve as a trademark.

The vitreous disk I2 is sufficiently thick to support the lead-in rods or wires 28 and the contact pins 28 to which the lead-in wires are electrically connected. In the broad aspect of my invention, the electrode assembly in the tube may be of any suitable construction or arrangement, depending on the function of the tube, which may be a detector, an amplifier, a rectifier, or operate for any other practical purpose. By way of example I have shown in Fig. 1 an electrode assembly E consisting of an electron-emitting fila` ment or cathode 38, a. grid 3|, and a cylindrical anode 32, all arranged and mounted in the usual way. For simplicity of illustration I have shown the electrode assembly supported on the rods 2l, but any other practical form of electrode support may be used. With this three-electrode assembly only four of the six contact pins 29 will be electrically connected to the electrodes. The vitreous disk I2 has as many holes 33 as there are lead-in wires 2l passing through it, and the contact pins 2! are in axial alignment with these holes. The enlarged view in Fig. 6 clearly shows how each wire 28 and its associated contact pin 28 are mounted in disk I2. 'I'he hole 33 has a circular shoulder 3l on which the round head 35 of pin 28 rests. The pin is preferably hollow for receiving the wire 28 in a close iit, and the two parts may be soldered together at the tip, as indicated at 36, to insure good electrical contact.

To seal each wire 28 and its pin 2B to disk I2, a small glass cylinder or sleeve 31 is placed around the wire in hole 33 and heat is applied uniformly around the glass sleeve, as by gas jets 38, until the glass melts and completely fills the hole around the wire 28 and the head 35 of contact pin 25. T'he fused condition of the glass sleeve 31 is shown at 31' in Figs. l and 2. I may form the disk I2 with an integral upstanding rim 39 around each hole 33 to hold the molten glass better in place and increase the depth of the seal. The glass seal 31 unites the wire 28 to the insulating disk I2 in a vacuum-tight weld, and is sufliciently strong to hold the wire and its contact pin rigidly anchored in the disk.

Figs. 'l and 8 illustrate other ways of securing the contact pins 23 to the vitreous disk I2. In Fig. l the head 35 of the pin is embedded in the disk while the latter is still plastic in the mold. That is to say, the contact pins are properly arranged in the mold, so that when the plastic material is poured in, the headed ends of the pins become embedded in the mass. When the hardened disk is then removed, the metal pins are permanent structural parts thereof. In Fig. 8 the molded disk I2 is formed with a circular recess I0 and a larger undercut recess or groove I I. The head 35 of pin 23 fits snugly in recess 4D and is locked in place by a ring l2 which fills the outer recess 4I. The ring I2 maybe glass, ceramic material, or any suitable cement. The glass seal 31' for wire 28 in Figs. 'I and 8 is formed as previously explained in connection with Fig. 6. One advantage of attaching the contact pins 29 to disk I2 as shown in Figs. 7-8 lies in the fact that the pins are held in place independently of the glass seal 31', so that any axial thrust against the pins in handling the tube is taken up by the disk itself instead of the glass seals that hold the lead-in wires.

The tube shown in Figs. 4-5 differs from that of Figs. 1-2 mainly in having the exhaust tip 42 sealed into the vitreous base disk I2 by an annular glass seal 44, which may be formed in the same way as the seals 31 of wires 28. The disk I2 may have an annular projection M' to provide a greater depth for seal 44. The exhaust tip 43 may be glass or metal; and if glass, it is preferably enclosed in a small sheet metal cup 45, the fianged head of which is embedded in the molded disk I2 by a cement ring Il in an undercut groove 41 at the bottom of the disk. The cup 45 may be noncylindrical or have an axial notch 48 adapted to receive a properly placed rib or lug in the tube socket to compel the correct mounting of the tube.

By putting the exhaust tip 43 in disk I2, the dome-shaped top 49 of the metal shell I0 is free to support a cap contact 50, which is used in certain types of radio tubes, as those familiar with that art will understand without more words. The top 49 is provided at the center with an integral tubular extension or nipple 5I, which terminates in a small funnel 52 with an opening for the conducting wire 53. The funnel 52 is filled with a fused seal 54 of glass or the like, which closes the top of the tube in a vacuum-tight joint. The metal cap 50 is secured over the nipple 5I by means of a suitable cement 55, which is an electric insulator, and the outer end of wire 53 is attached to the top of cap 50, which is completely insulated from the metal shell I0 by the inner glass seal 54 and the cement lining 55.

The electrode assembly E in Fig. 4 comprises a heating filament 56, a cathode 51 in the form of a hollow refractory rod through which the filament extends and which is coated with electronemitting material, an inner grid 58, a second grid 59, and an anode 60 in the usual form of a metal cylinder surrounding the other electrodes. A disk 6I of mica holds the upper ends of the electrode-supporting rods rigidly spaced, and a small insulating disk 62 spaces the lower ends of rods 63 that support the grid 59. The disk 62 is mounted on a metal plate 62' welded to rods 63. The lower end of conducting rod 64, which supportsvthe inner grid 58, is embedded in disk 62 and the upper end of the rod is connected with wire 53. The tubular cathode 51 passes through disk 62 and is rigidly connected by a cross piece 65 to the supporting rod 66. The mica disk 6| is perforated to permit the exhaustion of air from the upper space of the tube. It will be understood that any other practical electrode assembly may be supported in the tube to carry out the prescribed function thereof.

The glass sealing ring I8 in Fig. 4 may be applied as shown in Fig. 2 and previously described. 'I'he cylindrical flange 6l of the metal shell I0 in Fig. 4 has a hollow bead 68 which locks the fused seal I8 in place, and the disk I2 is locked to the seal by the undercut groove 69. Any other practical means may be employed for mechanically locking the united parts Ill-I 2-I8 together aside from the adhesion of the seal to the metal shell I0 and the vitreous disk I2, whereby the vacuumtight weld between those three parts is materially strengthened. What else was said about the seal I8 in Fig. 1 applies to the seal in Fig. 4 without the need of repetition.

I have mentioned that the insulating disk I2 may be of glass or a vitreous ceramic material like porcelain. If the disk is molded orpressed of glass, it is preferable to use a glass having a low coeilicient of expansion, say of the order of 0.000004, which is one of the properties of the borosilicate glasses. A particularly strong glass for disk I2 is a heat-proof glass like that described in Sullivan and Taylor Patent No. 1,304,623 granted May 27, 1919, this glass having an expansion coefficient even lower than the figure just given. Porcelain contains enough of a vitreous or glassy matrix to render it dense and non-absorbent like glass, so it is a suitable material for the disk I2. Although porcelain is fragile in thin pieces, the disk I2 is small and thick, so that it is practically unbreakable in combination with theaurrounding metal of sh'ell I0. It also may be noted that the expansion coeilicient of porcelain is about 0.000004, substantially the same as that of the borosilicate glass previously mentioned. Brieiiy, then, it may be said that the expansion coefiicient of the vitreous disk I2 is so low that the disk is practically unaffected by the working temperature of the tube. Hence, the electrodes remain in fixed relation to each other and the weld between the disk I2 and the fused ring Il remains vacuum-tight. By way of example I would say that in some cases the vitreous disk i2 may be about one inch in diameter and about one fourth of an inch thick across the main part, thus giving the tube a strong base which automatically lnsulates the lead-in wires 28 and contact pins 29 from. each other across the entire distance of their spacing.

The material of the sealing ring I8 should be a glass having an expansion coefficient equal or very close to that of disk I2, whether the latter be of glass or of porcelain. A glass having practically the same expansion coefficient as porcelain is readily obtainable or producible. With the members I2 and Il having substantially the same low coeicient of expansion, they become in effect a unitary base sealed to the metal shell I0. It does not matter that the expansion coeflicient of the metal shell is higher than that of the glass seal I8, since the heat-insulating propertles of the seal and of disk I2 prevent undue heat from reaching'the flange Il of the shell across the base of the tube. Besides, the anged baseportion of the metal shell I0 is outside the chamber of the tube and is therefore not directly subject to the inside temperature. The individual seals 31' for the lead-in wires 28 are preferably of glass with an expansion coeiiicient substantially equal to that of the wires.

The glass seals 81 will usually be made of a high expansion glass (like the glass of electric light bulbs), as that gives probably the best sealing results. However, if it is found desirable in any particular instance to make the seals 3l' of a low expansion glass, the Wires 28 should be 0f metal having a correspondingly low coeiilcient of expansion.

As an example of such metal I may mention alloys of iron and nickel having those two elements so proportioned-that the expansion coefficient of the resultant alloy also represents (or closely approximates) the expansion coeilicient of the glass used in seals 31'. For example, an alloy of, 54% iron and 46% nickel has about the same expansion coeicient as the glass used in electric light bulbs. An iron-nickel alloy known in the trade, comprising 63% iron and 37% nickel, has a coefficient of expansion so low as to be practically negligible, and in certain cases I may prefer to make the lead-in wires 28 of said alloy. By this I mean not only those sections of the wires that pass through disk I2, but also the upper sections to which the electrodes are secured. '-In Fig. 1 the grid cylinder 3l and the anode cylinder 32 are attached to rods 28 which may be integral with the corresponding rods 28 or (as shown) separate pieces welded to the upper ends of rods 28. The same remarks apply to the various electrode-carrying rods in Fig. 4. Not only the rods 28-28 but also the grids and the anode cylinder 32 (or 68) may be of the aforesaid iron-nickel alloy so as to remain unaffected by the temperature in the tube. That is to say, an anode consisting of a cylinder of an alloy containing aproximately 63% iron and 37% nickel does not expand under the heat of the tube chamber and therefore does not alter its normal diameter and position relative to the enclosed grid and cathode. This fixed relationship of the electrodes at all tube temperatures is a desirable factor.

In metal radio tubes heretofore made with a shell oi steel, it was found that after a while the inner surface of the steel gave oil! gases which deteriorated the vacuum in the tube and reduced its emciency. As iar as I know, no theory has been advanced for this phenomenon, but my study of this problem has led me to these conclusions: Commercial sheet metal, no matter how well polished or smoothed, has minute cells or pockets in its surface, due to the crystalline structure of the metal. This is particularly true of steel, which contains carbon. Also, metals take up gases in melting and doubtless very small amounts of these gases are retained in the tiny pores or cells of the solidified metal. Referring now to the metal shell of an electron tube, the multitudinous pores that happen to be on the inner surface of the shell occlude air and other gases present, and these trapped gases can not all be drawn out in the exhausting oi the tube, so that they remain in the evacuated chamber. Later, during the operation of the tube, the metal gradually gives up the occluded gases which naturally vitiate the vacuum and lessen the efiiciency of the tube.

I overcome the foregoing objection in prior electron tubes with a metal envelope or shell by electroplating the inner surface or the metal shell so as to ll in the air cells or pores and provide a metal surface of atomic density and smoothness substantially free of occluded gases. In the drawing the electroplated inner surface of metal shell I0 is diagrammatically indicated by numeral 10. The electroplating l0 may be nickel, copper, silver, chromium, and perhaps other metals found suitable for this purpose. The thickness of the electroplating should be suilicient to ll the cells or pores on the surface of shell Il) and cover it completely with a uniformly smooth and dense wall of pure metal in which no gases are occluded and which prevents the escape of gases that might lurk behind the electroplating.

If the base disk I2 is made of porcelain, it ma be desirable in some cases to glaze its inner surface, asis usually done with porcelain. This glazing, diagrammatically indicated by numeral 1I in the drawing, is a dense vitreous coating fused to the porcelain body of the disk and performs the same function as the electroplating 10 on the metal shell IIJ. It goes without saying that the glaze 1I should be in agreement with the thermal expansion characteristics of the porcelain used, so that no cracking of the glaze can occur. If the porcelain of disk I2 contains a glassy matrix suniciently large, the glaze 1I will not as a rule be necessary.

From what I have said it will be evident that the materials of metal shell III, vitreous disk I2, and glass seal I8 may be so chosen as to have practically the same low coeilicient of expansion, so that these three parts when sealed together form in eiect an integral envelope for the tube chamber. The sheet metal shell I0 can be made of an iron-nickel alloy having the same expansion coeilicient as the vitreous parts I2 and I8, and the inner surface of the alloy shell can be electroplated, as previously mentioned.

It is clear from the preceding description that I have produced an electron discharge tube of simple construction, easy to assemble, and one combining mechanical strength with electrical eillciency. Although I have shown and described certain specific constructions, my invention is not limited to the details set forth, for various changes and modifications are possible within rthe scope of the appended claims.

It is hardly needful to add that the accompanying drawing is not intended for a shop drawing and has not been made with the mathematical accuracy required in the latter. On the contrary, I have purposely exaggerated the relative dimensions of various parts for clearness.

I claim as my invention:

1. An electron tube having an outer envelope consisting of a metal shell and a vitreous base within the base end of the shell, a ring separate from and between the shell and the base airtightly uniting the shell and base, means independent of the sealing contact between said parts for positively locking the base to the metal shell against axial displacement in either direction, and an electrode assembly carried by said base.

2. An electron tube having a metal shell, a base member of insulating material, a glass ring uniting said base member with said shell, interlocking means on said ring and shell and base member to lock the latter against axial displacement in either direction, said interlocking means being independent of the sealing contact between the shell and the base member, and an electrode assembly carried by said base member.

3. An electron tube having a metal shell, a base member oi insulating material, a ring of vitreous material between and uniting the shell and the base member, said shell having an inwardly turned portion locking said ring against outward axial displacement relative to the shell, and an electrode assembly carried by said base member.

4. An electron tube having a metal shell, a disk comprising vitreous material, a vitreous sealing ring interposed between said shell and disk and sealed to both of said parts in wide annular contact areas, interlocking means between the shell and the ring to lock the latter against axial displacement in either direction, interlocking means between the disk and the ring to lock the disk against outward axial displacement, both of said interlocking means being independent of the sealing contacts made by the ring with the shell and the disk, and an electrode assembly carried by said disk.

5. An electron tube having a cylindrical metal shell provided at its lower end with an outer lateral shoulder, a ilange projecting downwardly from said shoulder, an insulating disk engaging said shoulder and spaced from said flange, the space between said ange and disk forming an annular recess, a fused vitreous ring filling said recess and sealed to said disk and shell, means for locking said disk and sealing ring to the shell against axial displacement in either direction, said locking means being in addition to the sealing contact between said three parts, and an electrode assembly carried by said disk.

6. In the manufacture of electron tubes having a metal shell and a base disk of insulating material, the method of sealing the shell and the disk together which comprises supporting the shell upside down, placing the disk on a shoulder of the shell so that an annular recess is left between the disk and the shell, placing a glass ring in said recess, which has a cross-sectional shape different from that oi' the glass ring, and heating the ring until it fuses and llows into the recess, whereby the fused mass seals the metal shell and the insulating disk together,l the cross-sectional shape of the recess causing the sealed parts to be locked together against relative axial displacement in either direction.

7. An electron tube including a cylindrical metal shell, an integral exhaust tip in the top of said shell, said tip'being surrounded by an annular depression formed in the shell, and a filler in said depression to hide the tip, said ller forming a domed top for the shell.

8. An electron tube having a base disk of vitreouslmaterial relatively thick, lead-in wires passing through said disk into the tube for connection with an electrode assembly, said disk being formed with a plurality of circular recesses extending only part-way into the disk,-there being a recess around each wire, and a vitreous seal lling each recess for sealing the surrounded wire to the disk, each wire closing the bottom of the surrounding recess which forms acup to hold the fused seal in place.

9. An electron tube having an envelope closed by a base disk of vitreous material formed with a plurality of recesses, said disk having an integral annular rim around each recess, a lead-in wire passing through each recess, a fused glass seal filling each recess and surrounding the associated .wire which is thereby sealed to the disk in a vacuum-tight joint, the annular rim around each recess increasing the axial depth of the glass seal and the stability of the wire support, and electrodes connected to said wires.

10. An electron tube having a cylindrical metal shell provided at the top with an integral metal.

exhaust tip which is surrounded by an annular depression in the shell, whereby said tip does not appreciably project beyond ythe wall surrounding said depression.

' 11. An electron tube having an envelope comprising a 'metal shell and a disk sealed to the base end of said shell, the top of said shell having a tubular projection with an opening sealed by a glass member, a lead-in wire sealed to and passing through said glass member into the envelope, a metal cap mounted over said tubular projection and insulated therefrom, said wire being connected to said cap, an electrode assembly operatively mounted in said envelope and including an element connected to said lead-in Wire, and contactpins projecting from the base end of the tube and operatively connected with saidelec-` trode assembly.'

12. An electron tube having a metal shell, a vitreous ring sealed to the base of said shell, a disk of low expansion glass sealed to said ring and closing the open end of said shell air-tight, said glass disk being suiilciently thick to be practically unbreakable, and an electrode assembly supported by said glass disk.

13. An electron tube having a 4base of insu lating material, -a contact pin mounted in an outer portion of said base, a lead-in wire extending from said contact pin through an'inner por-r tion of saidl base,'said base having a recess directly around said lead-in wire, and a ring of insulating material in said recess sealed, within said recess, at its inner side to the lead-in wire and at its outer side to the base .to maintain the tube air-tight regardless of any` air-,tightness between the contact pin and the base.

14. An electron tube as set forth in claim 13 in which the contact pin has a anged head' seated in the bottom of the recess and 'held seated therein by the ring of insulating material.

AD'oLPH A. momia. 

